This invention relates broadly to the field of transferring charge in a charge-coupled device (CCD), and more particularly, to a charge control circuit for bidirectionally transferring metered amounts of charge, selectively, in a CCD.
A description of a proposed charge-coupled device type adaptive signal processor exemplifying the utility of the present invention may be found in (1) a Paper entitled "CCD Analog Adaptive Signal Processing" authored by M. H. White, I. A. Mack, G. M. Borsuk, D. R. Lampe, and F. Kub, which was presented before the 1978 International Conference on the Application of Charge Coupled Devices at the Naval Ocean Systems Center, San Diego, Calif. from Oct. 25 through 27, 1978, pp. 3A-1 through 3A-14; and (2) a Paper entitled "Charge-Coupled Device (CCD) Adaptive Discrete Analog Signal Processing" authored by M. H. White et al., same author combination as Paper (1), which was presented in the IEEE Journal of Solid-State Circuits, Vol. SC-14, No. 1, February 1979. Signal processors of this type are proposed as using a so-called "clipped-data" least mean square (LMS) error algorithm to optimize the selection of tap weights in a CCD filter. The CCD filter may be comprised of a basic linear combiner formed with a nondestructively tapped CCD analog delay line and electrically reprogrammable MOS analog conductances as the tap weights. One method of varying the analog conductance of the MOS transistors in the proposed filters is to vary the gate voltage thereof while keeping the source and threshold voltage V.sub.T substantially fixed.
Both of the above Papers (1) and (2) proposed the use of a CCD bidirectional charge control weight adjustment for varying the V.sub.GS of each of the MOS transistors used as the tap weights. For more details, reference is made to pages 3A-6 and 3A-7 of Paper (1) and pages 137 and 138 of Paper (2). While the basic idea of bidirectionally controlling charge to provide a variable V.sub.GS on the gate of an MOS transistor has been proposed in the Papers (1) and (2) above, it is realized that these ideas were an alternate method of controlling the tap weights and were not used in the ultimate design of the adaptive filter as described in said Papers. In addition, it should be noted that the details of the structure of a bidirectional charge control circuit were not included in either of the Papers (1) or (2) referenced hereabove.
Carrying this one step further, it is well known that charge may be unidirectionally injected and transferred through a charge-coupled device for a large variety of applications. An example of one application is the adding or subtracting of charge in a holding well of a CCD structure as disclosed in U.S. Pat. No. 4,085,441, issued Apr. 18, 1978 and entitled "Monolithic Implementation of a Fast Fourier Transform"; refer more particularly to FIGS. 5 and 6 thereof. Another example of a unidirectional charge injection CCD application is disclosed in U.S. Pat. No. 4,112,456, issued Sept. 5, 1978 to Lampe et al. and entitled "Stabilized Charge Injector for Charge Coupled Devices with Means for Increasing the Speed of Propagation of Charge Carriers". However, neither of the proposed structures disclosed in these references suggested the idea of bidirectional charge transfer as discussed, generally, in the Papers (1) and (2) supra.
Since a need has been proposed for a bidirectionally charge-controlled circuit, then, the disclosure of at least one embodiment of such a circuit, especially for use in the charge-coupled device type adaptive signal processors described in connection with Papers (1) and (2) referenced hereabove, appears most desirable. Thus, it is the intention of the following specification to describe such a bidirectional charge control circuit for accurately incrementing and decrementing charge selectively to and from a charge storage medium.